1. Field of Invention
The present invention relates to a semiconductor device, and more particularly, to a light emitting diode (LED) chip.
2. Description of Related Art
LED chips are a kind of semiconductor device fabricated by chemical elements of group III-V, such as gallium phosphide (GaP), gallium arsenide (GaAs) and gallium nitride (GaN). By applying current to the compound semiconductors, and through the recombination of electrons and holes, the electric energy is converted into light energy and released in photon form to achieve light radiation. The radiation of a LED is of a cold mechanism, but not through heat, therefore the lifetime of LEDs can be over a hundred thousand hours and no idling time is required. In addition, LEDs have such advantages as fast response speed (about 10-9 second), small volume, low power consumption, low pollution (no mercury), high reliability and adaptation to mass production. Hence, LEDs have wide applications, such as light sources of scanners, backlight of liquid crystal displays, outdoor display boards, or vehicle lightings.
The conventional LED mainly comprises a light emitting layer, an n-type doped semiconductor layer, and a p-type doped semiconductor layer. The n-type doped semiconductor layer and the p-type doped semiconductor layer are disposed on two sides of the light emitting layer, respectively. Generally, there is lattice mismatch between each of the above material layers, which may cause the quality of the epitaxy to deteriorate due to the relatively large stress generated during the process of epitaxy. Furthermore, since the p-type doped semiconductor layer has a higher resistance value, a larger voltage drop may be occurred at the joint between the p-type doped semiconductor layer and the light emitting layer, thus a higher operation voltage is required for the LED.